In the salt lake industry, large amounts of steamed ammonia liquid waste are discharged as byproducts. The conversion of the residues into high value-added vaterite-phase calcium carbonate products for industrial applications is highly desirable. In this research, the feasibility of preparing vaterite-phase CaCO₃ in different CaCl₂-CO₂-MOH-H₂O systems using steamed ammonia liquid waste was studied in the absence of additives. The effects of initial CaCl₂ concentration, stirring speed and CO₂ flow rate on the composition of the CaCO₃ crystal phase were investigated. The contents of vaterite were researched by the use of steamed ammonia liquid waste as a calcium source and pure calcium chloride as a contrast. The influence of the concentration of CNH₃·H₂O/C_Ca²⁺ on the carbonation ratio and crystal phase composition was studied. The reaction conditions on the content, particle size and morphology of vaterite influence were discussed. It was observed that single vaterite-phase CaCO₃ was favored in the CaCl₂-CO₂-NH₄OH-H₂O system. Additionally, the impurity ions in steamed ammonia liquid waste play a key role in the nucleation and crystallization of vaterite, which could affect the formation of single-phase vaterite. The obtained results provided a novel method for the preparation of single vaterite particles with the utilization of CO₂ and offered a selective method for the extensive utilization of steamed ammonia liquid waste.

The objective of this study was to explore the influence of an alkali liquid accelerator based on sodium aluminate (ASa) on the early hydration behaviour of cement paste, tricalcium aluminate (C₃A) and tricalcium silicate (C₃S) and identify its accelerating mechanism. The setting times and mechanical properties of cement paste and mortar mixed with different amounts of ASa were determined. Isothermal calorimetry showed that the addition of ASa increased the first exothermic peak of cement hydration and advanced the second exothermic peak. The morphology of hydration products was analysed by scanning electron microscopy (SEM) and a model for the early hydration of cement paste was established. X-ray diffraction and SEM were also used to analyse the phase composition and morphology changes of C₃A and C₃S with or without ASa and early hydration models were established. Analysis of the experimental results revealed that the sodium hydroxide produced by ASa hydrolysis had the function of consuming gypsum, breaking calcium silicate hydrate gel film and increasing the calcium hydroxide concentration in the cement paste. The ettringite in the hydration products interweaved together to form a skeleton structure, which was conducive to cement paste hardening.